462 Geological Society : — 



By Lieut.-Gen. C. A. McMahon, Y.P.G.S., and Capt. A. H. McMahon, 

 CLE. 



In the first part of this paper Capt. McMahon describes briefly 

 the physical geography of the Baluchistan deserts, which extend 

 along the south of the Helmund Biver, between Quetta and Persia. 

 Taking first the plains and their drainage-system, he shows how 

 the wide alluvial plains of Shorawak and Chagai were probably in 

 earlier times one large lake. North and west of these plains, as far 

 as Persia, lie vast deserts of sand, which in places are gradually 

 encroaching upon and burying the mountain-ranges which rise up 

 like islands in the desert. He shows how the sand has intercepted 

 all the drainage from the mountains and prevented it from making 

 its way, as it would otherwise do, into the Helmund Biver and the 

 God-i-Zirreh Lake. Turning next to the mountains, Capt. McMahon 

 describes a well-defined line of fault, which he traced for a distance 

 of about 120 miles from north of Chaman, along the Khwaja Amran 

 and Sarlat mountain-ranges to Nushki. East of this fault all the 

 rocks appear to be sedimentary ; while those to the west are all, 

 with few exceptions, volcanic and igneous. 



The mountain-ranges in the desert described appear to be all 

 volcanic, and reference is made to the Koh-i-Taftan, 12,600 feet 

 high, lying south-west of them, which is still an active volcano. 

 The curious, grotesquely-shaped peaks of the Koh-i-Sultan range 

 are then briefly described, and especially that named Neza-i-Sultan 

 — a gigantic natural pillar of volcanic agglomerate many hundreds 

 of feet high. 



After thus describing the general character of the country, 

 Capt. McMahon points out the very remarkable force and activity 

 with which certain natural agents are at present at work there — 

 namely, water, wind, sand, and extremes of heat and cold. 



In the second part of the paper Gen. McMahon describes the 

 microscopical characters of the rocks, which consist of lavas, ashes, 

 pumice, igneous intrusive, and sedimentary rocks. The localities 

 in which ores of lead and copper, gypsum, sulphur, etc. occur 

 abundantly are also mentioned. 



Some andesites are described, which are especially interesting 

 from a petrological point of view. Bosenbusch mentions that a 

 brown hornblende occurs in some rocks in which the angle of 

 extinction varies from small to nil. Some of the andesites described 

 abound in amphibole, red-brown in transmitted light, which possesses 

 the optical properties and specific gravity of anthophyllite, and 

 which uniformly exhibits straight extinction. It is an original, and 

 not a secondary mineral. 



These anthophyllite-bearing augite-andesites also contain olivine 

 — a mineral rare, but not unknown, in this class of rocks. 



2. ' On the Association of Sigillaria and Glossopteris in South 

 Africa.' By A. C. Seward, Esq., M.A., F.G.S., University Lecturer 

 in Botany, Cambridge. 



3. ' Notes on the Occurrence of Sigillaria, Glossopteris, and 

 other Plant-remains in the Tnassic Bocks of South Africa. By 

 David Draper, Esq., E.G.S. 



